Solder ring for production of vacuum tube and method for the production of such a solder ring and of a vacuum tube

ABSTRACT

Solder ring ( 12 ) for joining two components ( 10, 11 ) of a vacuum tube, the solder ring ( 12 ) comprising a joining part that consists of solder material for forming an airtight joint between the two components. The solder ring ( 12 ) further comprises at least one centring part. The centring part has at least one first projection ( 14, 15 ) that extends on one side of the joining part essentially in an axial direction of the solder ring ( 12 ) and at least one second projection ( 13, 16 ) that extends in an opposing direction for centring the two components ( 10, 11 ) with respect to one another.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a solder ring for use in the production of avacuum tube and a method for the production of such a solder ring. Moreparticularly, the present invention relates to a solder ring accordingto the preamble of claim 9.

The present invention furthermore relates to a method for the productionof a vacuum tube and more particularly to joining the various componentsfor the vacuum tube to one another. Joining of the components to oneanother is effected with the aid of a hard solder that is placed betweenthe join locations.

2. Background Information

EP-A-0 204 145 describes a connection part for soldering two tubestogether. In one specific embodiment (see FIG. 2) the part is a solderring having two axially extending parts on opposite sides of the part.The radially extending parts are located at the outside edge of theconnection part.

A solder ring for use in the production of a vacuum tube is disclosed inGerman Patent Application DE-OS 39 31 774. This document describes avacuum tube where a solder ring is placed between the ceramic housingand an end cap for making an airtight joint between them.

For soldering components to one another it is important, especially whenfixing end caps to a ceramic housing, that said end caps are fixedproperly centered on the housing. If this is not the case there is thena possibility that the distances between live parts are no longeradequate and an electrical discharge can take place between those parts.High mechanical stresses can also be produced, which can result infailure of the ceramic.

In order to hold the components for soldering centered in the correctmanner, these are held together with the aid of jigs. The vacuum tubemade up in this way is placed in a furnace, after which, successively,the desired vacuum level is achieved with the aid of a vacuum pump andthe solder material is made to melt by heating, so that after cooling avacuum tube with the desired vacuum is obtained. Both the fitting andthe subsequent removal of the jigs must be carried out by hand. However,the use of jigs thus means that this method was not only laborintensive, but also that fewer made-up vacuum tubes can be processedsimultaneously in the furnace and that, because of the thermal capacityof the jigs, more energy is needed to achieve the desired temperature.Consequently, the final cost price of vacuum tubes produced in such away is very high.

In addition, the use of jigs means that differences in expansion arisebecause the jigs expand more than the ceramic of the vacuum tubes. Atconventional soldering temperatures this will result in a play of 0.5 to1 mm. This play is in addition to other tolerances that are customaryand thus gives rise to further impairment in the centering of thecomponents.

German Patent Application DE-OS 36 28 174 discloses a method with whichthe use of jigs is avoided by providing the ceramic housing of thevacuum tubes with an internal centering rim. Although the disadvantagesof the method using jigs no longer arise with this procedure, such acentering rim, however, makes the ceramic housing additionallyexpensive, as a result of which the cost price of the complete vacuumtube is thus also adversely affected.

In order to avoid the use of a centering rim in the ceramic housing, inthe cited publication it is further proposed to shape certain componentssuch that the desired centering is achieved by means of thesecomponents. However, as a result of the special shaping the productioncosts for these components becomes higher and this will also increasethe cost price of the vacuum tube.

The abovementioned DE-OS 39 31 774 also discloses a solution in whichthe components are shaped in such a way that the desired centering canbe achieved by this means. An additional disadvantage of such solutionsis that as a result of the physical contact between the components andthe inside of the ceramic housing the field strength is adverselyaffected, as a result of which the axial dimensions of the vacuum tubealso have to be larger. It will also have to be ensured that thefrictional forces generated by the centering in the ceramic housing arenot so large that these give rise to the problem that the componentconcerned is held back when the solder melts and is not able to makeadequate contact with the other joining surface, as a result of whichthe joint is not sufficiently strong.

SUMMARY OF THE INVENTION

The aim of the invention is, now, to provide a solder ring and methodfor the production of a vacuum tube with which the said disadvantagesare avoided and with which a vacuum tube is obtained at an appreciablylower cost price.

To this end, according to the present invention a solder ring of thetype defined in the preamble is provided, the solder ring furthercomprising at least one first projection being on an inside edge of thesolder ring and at least one second projection being on an outside edgeof the solder ring. The two components of the vacuum tube are, forexample, formed by an end cap and a housing. The end cap can be of anelectrically conducting material and the housing of a ceramic material.

Using a solder ring of this type it is possible to assemble and soldercomponents of a vacuum tube to be joined without an additional orseparate treatment and with this procedure the solder ring also providesfor the desired centering of the components. The joining part is shapedand sized in such a way that a joint of adequate mechanical strengthbetween the parts to be joined is obtained by this means and the solefunction of the at least one centering part is to enable the parts to bejoined to be assembled in a simple but correct manner and to be centeredand fixed with respect to one another. By centering the solder rings onthe inside of, for example, the housing made of ceramic, these ringswill, as a consequence of the unequal expansion, press firmly againstthe inside of the ceramic during heating. At the soldering temperatureemployed, a more accurate centering is achieved by this means.

This embodiment is simple to produce from existing solder rings, forexample by (partially) bending over the edge of the solder ring orcutting or punching the projections from the edge and then bending theseover.

In a further embodiment the at least one first and/or second projectionextend over the entire periphery of the solder ring. Such a ring can beproduced in a simple manner from a flat solder ring of the correctdiameter. In this case the width of the ring is approximately 50%greater than the width that is normally used and the thickness is thenapproximately 50% less than the thickness normally used. The at leastone first and/or second projection can then, for example, be formed byflanging the edge of the solder ring.

A further aspect of the present invention relates to a method for theproduction of a solder ring according to the present as defined in claim15. This is, in particular, applicable to already existing solder rings.As a result of forming the projections, the size (external diameterminus internal diameter) has to be chosen larger.

The method for the production of the solder ring can also comprise thestep of punching rings of a predetermined internal and external diameterfrom a strip-shaped piece of solder material. In a further embodimentthe punching and shaping can take place at the same time, for example bymeans for a follower stamp. The upright rims can then be made byflanging. The strip material that remains can be re-used by melting androlling it out again.

Yet a further aspect of the present invention relates to a method forthe production of a vacuum tube, comprising the steps of looselyassembling at least one housing, two end caps and two solder ringsaccording to the present invention, the solder rings being placedbetween the housing and the two end caps; applying vacuum to the looselyassembled vacuum tube; and heating the loosely assembled vacuum tube toa temperature at which the solder rings melt and respective airtightjoints form between the housing and the respective end caps of thevacuum tube, the solder rings providing for centering of the end capswith respect to the housing. Using this method it is possible to producevacuum tubes in a very inexpensive and efficient manner. Furthermore,accurate and simple centering of the various components with respect toone another is obtained.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present invention is explained in more detail below with the aid ofa few illustrative embodiments, with reference to the appended drawing.

FIG. 1 shows a partial section of a vacuum tube with the solder ringaccording to one embodiment of the present invention therein;

FIG. 2 shows a plan view of a solder ring according to a firstembodiment of the present invention;

FIG. 3 shows a cross-sectional view of the solder ring along the lineIII-III in FIG. 2;

FIG. 4 shows a plan view of a solder ring according to a secondembodiment of the present invention; and

FIG. 5 shows a partial cross-section of the solder ring of FIG. 4 alongthe line V-V.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A partial cross-section of an assembly of a housing 10, end cap 11 andsolder ring 12, which can be used to produce a vacuum tube, for examplefor an electrical vacuum switch, is shown in FIG. 1. The vacuum tube isaxisymmetrical and in general has two end caps 11, one at each end ofthe cylindrical housing 10. The housing 10 is frequently made of aceramic material that has a different coefficient of expansion to theelectrically conducting material of the end cap 11. For the vacuum tubeto function correctly, the end cap 11 and housing must be centered veryaccurately with respect to one another. With the embodiment of thesolder ring 12 shown this is achieved by a centering section of thesolder ring 12 formed by projections 13, 14 on the outside edge andinside edge, respectively, of the solder ring 12.

For production of the vacuum tube, the loosely assembled set of housing10, end caps 11, solder rings 12 and other components of the vacuum tubeare placed in a vacuum, for example a vacuum chamber. The whole is thenheated, so that the solder rings 12 melt and form an airtight jointbetween the housing 10 and the end caps 11. During the heating processthe solder ring 12 will press firmly against the inside of the (ceramic)housing 10 as a result of expansion. Accurate centering of the end caps11 with respect to the housing 10 is obtained as a result.

A first embodiment of a solder ring 12 according to the presentinvention is shown in FIGS. 2 and 3. In the plan view in FIG. 2 it canbe seen that the solder ring 12 has two projections 13 on the outsideedge and two further projections 14 on the inside edge. As can be seenin the cross-sectional view in FIG. 3, the projections 13 and thefurther projections 14 extend in opposing directions, essentiallyparallel to the axis of the solder ring 12. It will be clear to thoseskilled in the art that more or differently shaped projections 13, 14can be present.

A second embodiment of a solder ring according to the present inventionis shown in FIGS. 4 and 5. In this case the centering section of thesolder ring 12 is formed by two rims 15, 16 that are formed on theinside and outside, respectively, of the solder ring 12. This canclearly be seen in the partial cross-section in FIG. 5. The rims 15, 16extend in opposing directions, essentially parallel to the axis of thesolder ring 12.

In widely used designs for vacuum switches solder rings 12 with a widthof, for example, 11 mm, with an internal diameter of 49.5 mm and anexternal diameter of 58.5 mm can be used. The rims are, for example, 1.5mm high. The material of the solder ring 12 is, for example, 0.1 mmthick solder material. In a variant the internal diameter and externaldiameter are 49.5 mm and 56.5 mm respectively (width 7 mm) or 59.5 mmand 66.5 mm respectively (width again 7 mm).

A vacuum tube can be produced in a very simple and economical mannerwith the aid of a solder ring 12 according to the present invention.Instead of using jigs to hold the various components (in particularceramic housing 10, end caps 11 and solder rings 12) centered withrespect to one another during the production process, in the presentcase the whole can be loosely assembled. The loosely assembled set ofcomponents is then placed in a vacuum chamber and brought under vacuum.The set of components is then heated to a temperature at which thesolder rings 12 melt. During the heating process the ceramic housing 10and the metal end cap 11 will expand in different ways. As a result ofthe special shape of the solder rings 12 the various components will becentered and remain centered. After cooling, an airtight joint has beenproduced between the ceramic housing and the end caps 11, as a result ofwhich a vacuum tube is formed with high accuracy.

The solder rings 12 can be produced in a number of simple ways. Forinstance, conventional solder rings 12 (with somewhat modifieddimensions) can be provided with the projections 13, 14, for example bybending over (parts of) the inside edge and outside edge of the solderring 12, or by cutting out and then bending over the projections 13, 14.

In addition it is possible to produce the solder rings 12 from a stripof suitable solder material. In a first step, rings of the correctinternal and external diameter are then punched from the strip.Subsequently, for example, the upright rims 15, 16 are made by flanging.It is also possible to carry out the process of punching and bendingover in one process step, for example with the aid of a follower stamp,by means of which punching and pressing through is carried out at thesame time.

The solder material of the strip that remains after processing can bere-used by melting and rolling it out again.

1. Solder ring (12) for joining two components (10, 11) of a vacuumtube, the solder ring (12) comprising a joining part that consists ofsolder material for forming an airtight joint between the twocomponents, characterised in that the solder ring (12) further comprisesat least one centring part, the centring part having at least one firstprojection (14; 15) that extends on one side of the joining partessentially in an axial direction of the solder ring (12) and at leastone second projection (13; 16) that extends in an opposing direction forcentring the two components (10, 11) with respect to one another. 2.Solder ring according to claim 1, wherein the at least one firstprojection (14; 15) is on an inside edge of the solder ring and the atleast one second projection (13; 16) is on an outside edge of the solderring.
 3. Solder ring according to claim 1 or 2, wherein the at least onefirst and/or second projection (13, 14; 15, 16) extend over the entireperiphery of the solder ring (12).
 4. Solder ring according to claim 1,2 or 3, wherein the two components comprise at least an end cap (11) anda housing (10).
 5. Solder ring according to claim 1, 2, 3 or 4, whereinthe end cap (11) is made of an electrically conducting material and thehousing (10) is made of a ceramic material.
 6. Method for the productionof a solder ring (12) according to one of claims 1 to 5 comprising thesteps of forming the at least one centring part by bending over at leastone section (13, 14; 15, 16) of the inside and outside edge of a solderring (12).
 7. Method according to claim 6, comprising the further stepof punching rings (12) of a predetermined internal and external diameterfrom a strip-shaped piece of solder material.
 8. Method according toclaim 7, wherein punching and shaping take place at the same time bymeans of a follower stamp.
 9. Method for the production of a vacuumtube, comprising the steps of loosely assembling at least one housing(10), two end caps (11) and two solder rings (12) according to one ofclaims 1 to 5, the solder rings (12) being placed between the housing(10) and the two end caps (11); applying vacuum to the loosely assembledvacuum tube; heating the loosely assembled vacuum tube to a temperatureat which the solder rings (12) melt and respective airtight joints formbetween the housing (10) and the respective end caps (11) of the vacuumtube, the solder rings (12) providing for centring of the end caps (11)with respect to the housing (10).